I have two of these:
Turnigy 5000mAh 4S 14.8V 60C Hardcase Pack (AR Warehouse)
Good run time, but never timed it. Be warned - these are long packs, I had to trim the ears off the front of my battery tray to get them to fit.
I also have two of these that I run in series -
Turnigy nano-tech 5600mah 2S2P 50~100C Hardcase Lipo Pack (ROAR APPROVED) (US Warehouse)
They have more punch than the Turnigy batteries. Plus as a 2x2s, I can charge them both on my Prophet Sport Duo at the same time at 1C.
I also have one of these, for the rare occation I feel like breaking something - LOL
TH500065C6S Thor 5000mah 6S 22.2V 65C Lipo Pack
For budget packs, the Turnigy's I linked up top are about the cheapest 4s battery you can get with enough C to run the truck proper.
Next best budget lipo would be from SMC-Racing. They have great batteries for only a bit more then Hobby King. Better batteries than almost all the hobby king too - most of the racers in my area run SMC packs.
This pack will probably be my next battery purchase -
http://www.smc-racing.net/index.php?route=product/product&path=67_96&product_id=175
Also - watch for Hobby King sales. Several times a year they have big sales, and you can get select lipo's for about 50% off. That was how I got all of my HK packs. I think I paid $25 a pack for the Nano-techs, and $30 for the Turnigy packs. When they have the sale, it is normally only out of one warehouse, and they sell out quick.